Unlike other entities, fallingsand renders in real time, meaning that if there is massive tick lag, it will appear to be somewhere other than where it actually is. This doesn't happen with other entities.
Linked issues
Comments 3
Confirmed in 1.9. However, I discovered that there are a number of other things that also behave this way, so I'm going to merge them all into MC-76973. This report can be closed.
Fixed for 1.9